Short-term repeatability of hand-held keratometry measurements

Purpose. The Collaborative Longitudinal Evaluation of Ethnicity and Refract ive Error (CLEERE) Study is a multi-center, observational investigation of ocular component and refractive error development in schoolchildren. Anteri or corneal curvature is one of several ocular components which influence re fractive status of the eye, and the CLEERE Study uses the Alcon Auto-Kerato meter to measure corneal curvature, This report assesses the repeatability of this hand-held instrument. Previous studies have demonstrated the validi ty of the Alcon Auto-Keratometer; however, none have assessed its repeatabi lity. Methods. Sixty children were recruited from clinics affiliated with t he Southern California College of Optometry and the University of Houston C ollege of Optometry. Two sets of five hand-held keratometry measurements we re obtained on the right eye of each child by one investigator at each site using the Alcon Auto-Keratometer, The two sets of measurements were perfor med at least 10 minutes apart, Results. The mean differences between the tw o occasions were not significantly different from zero for either the flat or steep corneal curvature measurements regardless of the number of reading s taken. The largest improvement in repeatability, primarily for the steep meridian, occurred when the first two readings were averaged. The addition of readings 3, 4, and 5 to the average did not substantially improve repeat ability for either meridian. The 95% limits of agreement between the averag e of two readings on two occasions for the flat and steep meridians were +/ -0.28 and +/-0.39 D, respectively. The 95% limits of agreement after two re adings were +/-0.28, +/-0.20, and +/-0.24 D for the M, J0, and J45 vectors, respectively. Conclusion. The Alcon hand-held keratometer provides a repea table measure of corneal curvature as demonstrated by short-term repeat agr eement within +/-0.50 D. This level of repeatability can be achieved only b y manually averaging two consecutive measurements.